May 4, 2012
X-ray diffraction maps uniaxial strain in a single nanostructure
The continued downscaling in SiGe heterostructures has led to channels in which pure uniaxial strain is induced by lateral confinement. This provides strong enhancement of charge carrier mobility, which is sought by the electronics industry to improve device performance. In recent work, researchers in Italy have used X-ray diffraction to unveil and measure the uniaxial elastic strain of individual lithographically defined SiGe nanostructures.
The team fabricated one- and two-dimensional nanostructures from a strained SiGe layer. An X-ray beam focused down to a width of 100 nm was used to map the reciprocal space while scanning across individual nanostructures. The in plane and out-of-plane strain components were obtained by combining the diffraction data with kinematic simulations of the strain state based on finite element modelling of the nanostructures.
This method extends the technique of X-ray diffraction to individual nanostructures, commonly recorded using wide beams and requiring large ensembles of identical and ordered structures. The scientists found that nanopatterning allows a pure elastic anisotropic strain relaxation, which leads to conversion of the strain state from biaxial to uniaxial.
These results impact on the development of new-generation high-speed electronic devices, where the control of uniaxial strain in dislocation-free SiGe stressors could provide an efficient method of enhancing the carrier mobility in pure silicon transistor channels.
More information can be found in the journal Nanotechnology.
About the author
Researchers from the Politecnico di Milano, Italy, are the main contributors to the work: D Chrastina is a researcher at the L-NESS lab, G M Vanacore recently concluded his PhD at the SAM lab working with A Tagliaferri, researcher and principal investigator. The team is active in the development of smart nanostructured materials and their characterization. The current study results from the sharing of expertise and capabilities in several fields: semiconductor epitaxy (LEPECVD), scanning probe microscopy, electron microscopy and lithography in the Dipartimento di Fisica at the Politecnico di Milano and nano-beam X-ray diffraction at the ID13 ESRF beamline.